1. Field of the Invention
The present invention relates to an optical cross-connect device and an optical network, and in particular to an optical cross-connect device and an optical network utilizing a wavelength division multiplexing (WDM) system.
As speeds and volumes of information increase, broader bandwidths and larger capacities are demanded for networks and transmission systems. One of the means to implement this is an optical network based on wavelength division multiplexing technology, and an optical cross-connect device to be the core in constructing this optical network.
2. Description of the Related Art
FIG. 40 shows a general arrangement of an optical cross-connect device and an optical network including the same. An optical cross-connect device (optical XC) 100 accommodates a plurality of input/output light transmission lines (optical fibers) L2 and L3, and routes light signals which are wavelength division multiplexed and inputted from the input side light transmission line L2 to the desired output side light transmission line L3 for each wavelength or for each transmission line.
When inter-office links of the optical cross-connect device 100 are long distance transmission lines including light transmission lines L1 and L4 as shown, light amplifiers A1-A4 are inserted, as shown. The optical cross-connect device 100 is also connected to other communication devices, such as an electrical cross-connect device (electrical XC) 200 through a light transmission line L5, which is an intra-office link (link within office). These devices are controlled by an operation system OPS, which manages the entire network.
FIG. 41 shows an arrangement of the optical cross-connect device 100 shown in FIG. 40, where the optical cross-connect device is a wavelength switching-type.
In other words, light signals which are wavelength division multiplexed at wavelengths λ1-λn and inputted from the inter-office (in between offices) input side light transmission line L2 are demultiplexed into each wavelength by a wavelength demultiplexer WD1, and are provided to the first reproducing portion (opto/electro/opto conversion) RP1. The first reproducing portion RP1 once converts the light signals inputted from the inter-office light transmission line L2 into electric signals, reproduces the signals, and then converts the reproduced electric signals into light signals again to be transferred to an Ln*Ln light switch 150.
The light switch 150 routes light signals of input ports to desired output ports for each wavelength. The routed light signals are reproduced by a second reproducing portion RP2, and are further wavelength division multiplexed by a wavelength multiplexer WD2 to be outputted to the output side light transmission line L3.
When an optical network is constructed using such an optical cross-connect device that switches by the wavelength, large scale light switches with several thousands to ten thousand ports are required to accommodate enormous Internet traffic. For this, a technology to construct an optical network by combining the optical cross-connect devices for switching by the wavelength and fiber (transmission line) switching-type optical cross-connect devices for switching by the light transmission line has been used.
FIG. 42 shows such an optical network where the optical cross-connect devices for switching by the wavelength and the optical cross-connect devices for switching by the transmission line are combined. As shown, when a path is connected from an intra-office device (device within office) 1 to an intra-office device 1 in another office (another node), optical cross-connect devices (wavelength XC) 301-304 for switching by the wavelength are provided.
Output signals of the wavelength switching-type cross-connect devices 301-304 are connected to optical cross-connect devices XC#1-XC#4, which switch by the fiber respectively through a reproducer 2 and a wave multiplexer/demultiplexer (hereinafter, occasionally referred to simply as “multiplexer” or “demultiplexer”) 3 having a dual function of a wave multiplexer and a wave demultiplexer.
Moreover, the optical cross-connect devices XC#1-XC#4 are interconnected with inter-office transmission lines. In the example shown in FIG. 42, the optical cross-connect devices XC#1 and XC#2 are interconnected with an optical fiber F21, the optical cross-connect devices XC#1 and XC#3 are interconnected with an optical fiber F11, the optical cross-connect devices XC#2 and XC#4 are interconnected with an optical fiber F32, and the optical cross-connect devices XC#3 and XC#4 are interconnected with an optical fiber F53, respectively.
Portions drawn by dotted lines in FIG. 42 are shown as removed therefrom assuming a case where traffic is low, so that the number of transmission lines is minimized.
Therefore, when a path is established from an intra-office device 1_11, such as a router, to an intra-office device 1_21 in another office, for example, as shown, a path {circle around (1)} with the wavelength λ1 connected to the intra-office device 1_21 of another office is formed through the wavelength switching-type optical cross-connect device 301, the reproducer 2, the wave multiplexer 3, the fiber switching-type optical cross-connect device XC#1, and optical fiber F21, further through the fiber switching-type optical cross-connect device XC#2, the wave demultiplexer 3, and the reproducer 2 as well as the wavelength switching-type optical cross-connect device 302.
Also, in the case of the illustrated optical network, the number of optical fibers is minimized and the light signals with different destinations are routed by the fiber switching-type optical cross-connect devices XC#1-XC#4, so when signals are transmitted from the intra-office device 1_11 to intra-office devices in other offices (hereinafter, occasionally referred to simply as “intra-office device” or “device in another office”) 1_21, 1_31 and 1_41, the light signals with the wavelengths λ1 and λ2 pass through the optical cross-connect device XC#1, the optical fiber F11, and the optical cross-connect device XC#3, then pass through the wave demultiplexer 3 and the reproducer 2, and then light signal components with the wavelength λ1 are transferred from the optical cross-connect device 303 to the intra-office device 1_31.
On the other hand, the light signal components with the wavelength λ2 are looped back by the optical cross-connect device 303 and returned to the optical cross-connect device XC#3 with the wavelength converted into the wavelength λ3 transmitted along with light signals with the wavelengths λ1 and λ2 from the intra-office device 1_31 through the optical fiber F53, the optical cross-connect device XC#4, the wave demultiplexer 3, and the reproducer 2. Only light signal components with the wavelengths λ1 and λ2 are transferred from the optical cross-connect device 304 to the intra-office device 1_41.
Along with the light signal components with the wavelength λ1 from the intra-office device 1_41, the light signal component with the wavelength λ3 are passed through the optical cross-connect device 304, further converted again into wavelength λ2 by the reproducer 2, and a path {circle around (2)} for transferring the light signals from the optical cross-connect device 302 to the intra-office device 1_21 in another office through the wave demultiplexer 3, the optical cross-connect device XC#4, the optical fiber F32, the optical cross-connect device XC#2, the wave demultiplexer 3, and the reproducer 2, is formed.
In this way, insufficiency of the optical fibers is compensated for by the optical cross-connect devices 301-304 switched by the wavelength.
FIG. 43 shows the case when traffic is increased in the optical network shown in FIG. 42, where the intra-office device 1, the reproducer 2, the wave multiplexer/demultiplexer 3, and the optical fibers F12, F31, F51 and F52 are added, and paths are edited using the wavelength switching-type optical cross-connect devices 301-304 so that traffic (light signals) for each destination is accommodated in one transmission line when traffic for each destination increases to the extent of the number of wavelengths of the optical fiber.
In the example of FIG. 43, a total of 8 optical fibers are sufficient to be provided. FIG. 44 shows the number of required optical fibers assuming a case of 16 optical cross-connect devices. Numerals inside the parentheses show numbers of working fibers when no fault occurs, and numerals outside the parentheses show fiber numbers, including numbers of protective fibers required during a fault.
In the case of a conventional optical cross-connect device and optical network, as traffic increases, the device scale of the wavelength switching-type optical cross-connect device which routes the light signals of the intra-office device becomes large, and paths must be re-edited by the wavelength switching-type optical cross-connect device as necessary, so the paths in use must be switched, which causes an instantaneous disconnection of the paths.